Okay, let's break down your concerns about the marina electrical design. You're right to be thinking critically about these aspects, as safety and reliability are paramount in marina installations.

Concern 1: Nuisance Tripping with 100mA GFCI Protection You are correct to be concerned. 100mA is the maximum tripping threshold allowed in marinas as per NEC 555.3. With eight boats potentially drawing current on a single 125A feeder protected by a 100mA GFCI, nuisance tripping is a very real possibility. Marine electrical systems can be notoriously "leaky" due to the harsh environment, grounding practices on boats, and potential galvanic corrosion issues. Even small amounts of leakage from each boat can add up to a trip. The issue is cumulative leakage current. Each boat connected to the shore power has the potential to introduce a small amount of leakage current to ground. This current can be caused by insulation breakdown, moisture intrusion, or even intentional grounding practices within the boat's electrical system. The leakage current from each boat sums together. Once the cumulative leakage current exceeds the GFCI trip threshold (100mA), the breaker trips. Modern Electronics and Leakage

Modern boat electronics, particularly variable frequency drives (VFDs) for air conditioning or other equipment, can introduce significant leakage current even when functioning correctly. These VFDs often have internal filters that capacitively couple the AC power to ground, creating a path for leakage current.

Concern 2: Minimizing Feeder Size for Fault Hazard Reduction You are also correct to consider this. While larger feeders provide more capacity, they also increase the potential for a larger fault current if a short circuit occurs on the dock. A larger fault current can lead to more significant damage to equipment and increased risk of fire or electrocution. Arc Flash Hazard

In the event of a fault, a larger fault current also increases the potential for a dangerous arc flash. Arc flash incidents can cause severe burns, blindness, and even death.

Trade-Offs

There's a balance to be struck between providing adequate capacity for the boats and minimizing the potential for fault hazards.

Your Proposed Solution: One 30A, 120/208V Circuit per Pedestal Advantages



Reduced Nuisance Tripping

Significantly reduces the likelihood of nuisance tripping because you're limiting the number of boats per GFCI device to one.

Lower Fault Current Potential

Reduces the potential fault current if a short circuit occurs.

Easier Troubleshooting

Isolating each pedestal to its own circuit makes it much easier to identify and troubleshoot electrical problems.

Disadvantages



Increased Cost

This design will require more breakers, more wiring, and more labor to install.

Higher Panel Size

Requires more space in the electrical panel(s) for all the additional breakers.

Recommendations (Combining Both Your Concerns)


Definitely move towards smaller, dedicated circuits per pedestal. Your proposal of one 30A, 4-wire 120/208V circuit per pedestal is a much safer and more reliable design. It's the best way to minimize nuisance tripping and reduce fault current potential.2. Consider Metering at each Pedestal

Installing individual meters at each pedestal will allow you to accurately bill each boat owner for their electricity usage. It also provides valuable data for monitoring the overall electrical demand of the marina. You could use a smart meter which would also allow for monitoring current draw, and even remote shutoff if needed.3.

Use High-Quality GFCI Breakers

Invest in high-quality GFCI breakers specifically designed for marine environments. These breakers are typically more robust and less susceptible to nuisance tripping. Look for breakers with a high withstand rating and good surge protection.4.

Implement Proper Grounding and Bonding

Ensure that the grounding and bonding system is installed according to NEC Article 555 requirements. Use properly sized grounding conductors and make sure all metal parts of the dock are effectively bonded together.5.

Regular Inspections and Maintenance

Implement a regular inspection and maintenance program to identify and address any potential electrical problems before they become a hazard. This program should include visual inspections, electrical testing, and cleaning of electrical connections.

Bonding of Non-Current Carrying Metal Parts (NEC 555)



Your question about sizing up from #8 for bonding is valid. NEC 555.7(A) requires that all metal parts of the marina's electrical system and the dock structure be bonded together to form an equipotential plane. The size of the bonding conductor must be based on the size of the largest feeder supplying power to the dock. Specifically, NEC 555.7(A)(2) states

"Bonding conductors shall be copper, corrosion resistant, and sized in accordance with Table 250.122. The bonding conductor shall be sized on the basis of the largest overcurrent device that feeds the service, feeder, or branch circuit."

For your 125A feeders, you MUST size the bonding conductor according to Table 250.122 based on 125A overcurrent protection. Looking at Table 250.122, a 125A overcurrent protective device requires a #6 AWG copper bonding conductor. You are absolutely correct to consider this. #8 AWG would be insufficient.

Regarding Aluminum Dock Structure



Aluminum requires special attention to bonding and corrosion prevention. Ensure that all connections to the aluminum dock structure are made with corrosion-resistant hardware and that the connections are properly coated to prevent galvanic corrosion. Aluminum is anodic to most other common metals and therefore will corrode easily in the presence of moisture if not properly isolated. This can cause the bonding conductors to become loose and ineffective over time.

In Summary:

While the design of 125A circuits feeding multiple pedestals can* be done, it is not ideal for a marina environment due to the high risk of nuisance tripping and the potential for larger fault currents. Moving to smaller, dedicated circuits per pedestal significantly improves the safety and reliability of the electrical system. Also, don't forget to ensure that the bonding conductors are properly sized and installed to meet the requirements of NEC Article 555.I strongly recommend discussing your concerns and proposed solutions with the project engineer and the marina owner. Explain the reasons why you believe the current design is not optimal and how your proposed changes will improve safety and reliability. While there may be a higher upfront cost, the long-term benefits of a well-designed and properly installed marina electrical system will far outweigh the initial investment.Good luck with your bid! Remember that safety and reliability are the most important considerations in marina electrical design. Flag for review